This invention relates to a wrist mechanism capable of transmitting an angle to any direction as desired, and, more particularly, to a wrist mechanism suitable for use with an industrial robot.
A principal object of a wrist mechanism of an industrial robot lies, for example, in a realization of controlling the posture of a tool secured to or gripped by the wrist. When operations are performed by inserting a wrist in a narrow space, the wrist mechanism is required to have flexibility.
In providing a flexible wrist mechanism, resilient members may be used however a flexible wrist mechanism of this construction suffers the disadvantages that limitations are placed on the weight of an article to be carried by the wrist and positioning of the wrist itself cannot be effected with accuracy.
Thus, a flexible wrist mechanism of practical use would be composed of a plurality of rigid members connected together in a manner so as to be able to vary their angular relation whereby the mechanism as a whole could be deformed into a curved shape.
Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The word a "finger bone" or "link" will refer to each of the members of the mechanism connected together for relative angular displacement, and the word a "joint" or "junction" will refer to each of the connections between the finger bones.
Needless to say, a flexible wrist mechanism of the aforesaid construction could be realized by providing means separately for driving each of the finger bones. More specifically, a mechanism has been proposed which has a swing motor mounted in each joint, or has finger bones connected together by wires which, in turn, are connected to drive means, such as cylinders, for driving the respective finger bones.
In this type of flexible wrist mechanism, it is not essential that relative angular displacements of the finger bones be independently controlled. In many applications, the flexible wrist mechanism can function satisfactorily by causing all the finger bones to undergo relative angular displacements in an equal amount or in a certain ratio so that the mechanism as a whole can be displaced to form a substantially arcuate shape. In this case, it would not be advantageous to provide drive means for the finger bones independently of one another to obtain angular displacement of each finger bone. It would rather be preferable to minimize the number of the drive means or to use, if possible, the same number of drive means as the degrees of freedom possessed by one junction of the wrist mechanism so that angular displacement can be transmitted to the fingers purely by the action of the mechanism.
In, for example Japanese Patent Application Laid-Open No. 111158/77 and Japanese Utility Model Publication No. 46471/80 it has been proposed to provide mechanisms for enabling a realization of a flexible wrist mechanism. The former application has links connected together as by universal joints into a chain shape, with every other link being pivotally connected to transmit an angular displacement. In the latter, application links are connected together by spherical joints and the link which is located at the end or top of the wrist is connected to wires so that an angular displacement can be successively transmitted to the links by driving the wires.
Some disadvantages are associated with these mechanisms of the prior art. Difficulties are faced with in accurately transmitting an angular displacement between the adjacent links, and the mechanism has to be of complex construction or special construction.